Merge branch 'clean-up-pre-c++98-compatibility-macro' of https://github.com/minoki/wxWidgets

Don't bother with checking for some really obsolete compilers and just assume
that C++98 keywords "explicit", "{static,const,dynamic}_cast" and support for
partial template specialization is always available.

Closes #17655.

docs/doxygen/overviews/refcount.h

@@ -108,7 +108,7 @@ class-specific shared data. For example:
 @code
 MyClassRefData* GetData() const
 {
-    return wx_static_cast(MyClassRefData*, m_refData);
+    return static_cast<MyClassRefData*>(m_refData);
 }
 @endcode